Brigthest Cluster Galaxies

1. Brigthest Cluster Galaxies • most luminous • most massive • extended source → cD galaxy - only in clusters - Lvs cluster properties also giant E and D galaxy Unique classof objects • strong offset from FP but little scatter  different formation history • Close to the peak of the cluster X-Ray emission • some BCG shows multiple nuclei → galaxy merger Statistical study of parsec scale properties of a complete sample of BCGs is fundamental. BCG in Radio Band They are more likely to host radio-loud AGN than other galaxies of the same mass Our project Abell Clusters with DC ≤ 2 and Declination > 0 deg. (Best et al. 2006) Outside the Sample.... (to increase the statistic) Abell Clusters but with DC>2

2. E X T E N D E D S A M P L E NB: WAT in non cool core clusters (Owen et al. 1985) -5 GHz VLBA observations  new for 23/27 sources NB: Core+halo in cool core clusters (Burns 1990)

3. From our complete sample (nearby clusters) and literature data (Liuzzo et al. 2010) Strong dichotomy Cluster morphology # two-sided one-sided point N.D. BCG in relaxed clusters: 10 7 (70%) - 1 (10%) 2 (20%)‏ BCG in merging clusters: 22 - 13 (59%) 1 (5%) 8 (36%)‏ Not detected sources are mostly BCGs with a radio quiet core also in VLA images Comparison sample: Bologna Complete Sample: no selection effect on jet velocity and orientation 27% of FR I radio galaxies (same radio power range of BCG) have a two-sided jet  random angle distribution of sources with relativistic (Liuzzo et al. 2009). • FR I not BCG and BCG in merging clusters similar pc scale properties relativistic effects in intrinsically symmetric jets. • BCG in cooling clusters different pc scale properties  mildly relativistic jets  interaction with the surrounding medium ? 15 GHz VLBA Why/how mildly relativistic pc-scale jets in cooling clusters? 86 GHz VLBA Rossi et al. 2008 model • Ratio between ISM and jet density is important for pc scale jet deceleration CO emission  Dense ISM 3C 84